The inner regions of protoplanetary disks

TL;DR

This paper reviews recent advances in understanding the structure and physics of the innermost regions of protoplanetary disks, which are crucial for planet formation but difficult to observe and model.

Contribution

It provides a comprehensive overview of the history, recent developments, and challenges in studying the inner AU of protoplanetary disks using infrared interferometry.

Findings

Infrared interferometry has enabled direct spatial resolution of the inner AU.

Models of the inner disk regions are partly confirmed but also raise new questions.

Numerical modeling of these regions remains highly challenging.

Abstract

To understand how planetary systems form in the dusty disks around pre-main-sequence stars a detailed knowledge of the structure and evolution of these disks is required. While this is reasonably well understood for the regions of the disk beyond about 1 AU, the structure of these disks inward of 1 AU remains a puzzle. This is partly because it is very difficult to spatially resolve these regions with current telescopes. But it is also because the physics of this region, where the disk becomes so hot that the dust starts to evaporate, is poorly understood. With infrared interferometry it has become possible in recent years to directly spatially resolve the inner AU of protoplanetary disks, albeit in a somewhat limited way. These observations have partly confirmed current models of these regions, but also posed new questions and puzzles. Moreover, it has turned out that the numerical modeling of these regions is extremely challenging. In this review we give a rough overview of the history and recent developments in this exciting field of astrophysics.